A typical prior art disk drive system 10 is illustrated in FIG. 1. In operation the magnetic transducer 20 is supported by the suspension 13 as it flies above the disk 16. The magnetic transducer 20, usually called a “head” or “slider,” is composed of elements that perform the task of writing magnetic transitions (the write head 23) and reading the magnetic transitions (the read head 12). The electrical signals to and from the read and write heads 12, 23 travel along conductive paths (leads) 14 which are attached to or embedded in the suspension 13. The magnetic transducer 20 is positioned over points at varying radial distances from the center of the disk 16 to read and write circular tracks (not shown). The disk 16 is attached to a spindle 18 that is driven by a spindle motor 24 to rotate the disk 16. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films 21 include ferromagnetic material in which the write head 23 records the magnetic transitions in which information is encoded.
The conventional disk 16 consists of substrate 26 of AlMg with an electroless coating of NiP which has been highly polished. Glass is also commonly used for the substrate 26. The thin films 21 on the disk 16 typically include a chromium or chromium alloy underlayer which is deposited on the substrate 26. The ferromagnetic layer in the thin films is based on various alloys of cobalt, nickel and iron. For example, a commonly used alloy is CoPtCr. Additional elements such as tantalum and boron are often used in the magnetic alloy. A protective overcoat layer is used to improve wearability and corrosion. The three film disk described above does not exhaust the possibilities. Various seed layers, multiple underlayers and laminated magnetic films have all been described in the prior art.
In particular, seed layers have been suggested for use with nonmetallic substrate materials such as glass. Typically the seed layer is a relatively thin layer which is the initial film deposited on the substrate and is followed by the underlayer. Materials proposed for use as seed layers include chromium, titanium, tantalum, Ni3P, MgO, carbon, tungsten, AlN, FeAl, RuAl and NiAl. In U.S. Pat. No. 5,789,056 to Bian, et al., the use of a CrTi seed layer is described. The underlayers mentioned are Cr, CrV and CrTi.
In U.S. Pat. No. 6,010,795 to Chen, et al. a magnetic recording medium is described which has a surface oxidized seed layer (such as NiP), a Cr-containing sub-underlayer, a NiAl or FeAl underlayer and a Cr-containing intermediate layer on the NiAl or FeAl underlayer. The underlayer is said to have a (200) crystallographic orientation.
A MgO seed layer is disclosed in U.S. Pat. No. 5,800,931 to Lee, et al. A B2 structure underlayer, preferably NiAl or FeAl., is used along with an optional thin Cr or Cr alloy intermediate layer between the underlayer and the magnetic layer.
In published U.S. application 20010024742, Bian, et al. described a RuAl seed layer deposited directly onto a pre-seed layer and an optional layer of NiAl following the RuAl. This double layer configuration could result in cost savings by reducing the amount of Ru required to form the seed layer. Ru is an expensive element so a reduction in the required quantity of Ru reduces the costs. In the double layer structure the RuAl seed layer establishes the grain size and orientation and the subsequently deposited NiAl follows the established patterns.
Continued improvement in the magnetic recording properties is needed to further increase the areal recording density for magnetic media.